In the field of printing, the most common type of printer has been the printer which impacts against record media that is caused to be moved past a printing line or line of printing. As is well-known, the impact printing operation depends upon the movement of impact members, such as print hammers or wires or the like, which are typically moved by means of an electromechanical system and which system enables precise control of the impact members.
In the field of dot matrix printers, it has been quite common to provide a print head which has included therein a plurality of print wire actuators or solenoids arranged or grouped in a manner to drive the respective print wires a very short, precise distance from a rest or non-printing position to an impact or printing position. The print wires are generally either secured to or engaged by the solenoid plunger or armature which is caused to be moved such precise distance when the solenoid coil is energized and wherein the plunger normally operates against the action of a return spring.
In the wire matrix printer, the print head structure may be a multiple-element type with the wire elements aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in line manner, while the drive elements or transducers may be positioned in a circular configuration with the respective wires leading to the front tip of the print head.
Alternatively, the printer structure may include a plurality of equally-spaced, horizontally-aligned single-element print heads which are caused to be moved in back-and-forth manner to print successive lines of dots in making up the lines of characters. In this latter arrangement, the drive elements or transducers are individually supported along a line of printing. These single wire actuators or solenoids are generally tubular or cylindrically shaped and include a shell which encloses a coil, an armature and a resilient member arranged in manner and form wherein the actuator is operable to cause the print wire to be axially moved a small precise distance in dot matrix printing. The print wire is contained and guided at the front of the solenoid in axial direction during the printing operation. It is in the field of print wire actuators that the subject matter of the present invention is most closely associated and which provides for improved positioning and control of the print wire during printing operations.
While the conventional actuator of the type utilizing magnetic energy, such as the solenoid, is widely used, its low electro-mechanical conversion efficiency is a disadvantage when compared with a piezoelectric crystal element actuator utilizing the piezoelectric effect which permits a highly efficient electro-mechanical conversion.
Representative documentation in the field of dot matrix print head wire actuators includes U.S. Pat. No. 3,473,466, issued to L. C. Thayer on Oct. 21, 1969, which discloses an electrostrictive print hammer actuator, in the form of a bar-shaped piezoelectric crystal for driving a print hammer that is held in position by two upstanding flat springs in essentially free-flight manner against a type wheel.
U.S. Pat. No. 3,843,898, issued to E. T. Maciag on Oct. 22, 1974, discloses a piezoelectric mounting with variable damping wherein the piezoelectric element is freely suspended by contact springs and the mounting includes rigidly positioned damping means and movable damping means.
U.S. Pat. No. 3,940,726, issued to A. H. Gerschnow on Feb. 24, 1976, discloses a high speed solenoid having an armature initially driven against the biasing force of a weak spring. Just before impact, the armature is biased by a spring having a greater spring force to return the armature to the non-impact position.
U.S. Pat. No. 4,014,425, issued to W. A. H. Gijzen et al. on Mar. 29, 1977, discloses a recording element including a stylus and having an armature subject to action of a coiled spring that has two end sections with closely wound turns and an axial section with an inside diameter larger than the diameter of the stylus.
U.S. Pat. No. 4,157,873, issued to M. Ito on June 12, 1979, discloses a ferromagnetic core and a leaf spring biasing the core and deformed by a stopper. An annular washer is provided between the stopper and a shoulder of the housing and a coiled spring urges the washer against the shoulder.
U.S. Pat. No. 4,200,401, issued to K. L. Roy et al. on Apr. 29, 1980, discloses a print wire solenoid having an armature and a retraction spring anchored to a plastic body and positioned with respect to a datum surface. A rebound disc is positioned to locate the datum surface of the armature in the same plane as the datum surface of the stator assembly.
U.S. Pat. No. 4,236,837, issued to A. H. Seilly on Dec. 2, 1980, discloses an operating mechanism with a preloaded spring acting on the armature wherein the inertia only of the armature and the print wire causes impact of the wire on paper.
U.S. Pat. No. 4,490,057, issued to J. W. Reece on Dec. 25, 1984, discloses a solenoid having an enclosure member releasably secured to one end by a deformed spring member and an energy absorbing member adjacent the enclosure member. A plunger member is located adjacent and engaging the absorbing member during rebound movement to transmit forces to the enclosure and the spring member.
U.S. Pat. No. Re. 31,813, issued to P. E. Fugate et al. on Jan. 22, 1985, discloses a solenoid having a rebound and energy absorbing arrangement which uses a block of dead elastomeric material held in a partially compressed state by an impact plate.
And, U.S. Pat. No. 4,632,580, issued to R. L. Wirth et al. on Dec. 30, 1986, discloses a dampening mechanism which uses a single injection molded plastic piece with a plurality of plunger backstops arranged in a circle and spring hinged for impact against a rubber damper.
The principle of using a multi-layered type actuator is disclosed in the Institute of Electronics and Communication Engineers of Japan Technical Report, Vol. 84, No. 289, EMC 84-49, issued on Feb. 15, 1985.